This invention relates to lens systems for use in connection with providing vision through media having different indices of refraction, and in particular to lens or mask systems for use in diving and providing vision under water.
While underwater face masks have been in use for some time, nevertheless entirely satisfactory results have not been obtained. Most commonly, divers use a face mask merely to keep the water away from the eyes. Such a mask has generally included a flexible face piece, preshaped to fit closely against the face of the wearer, positioned in front of the eyes, and usually also over the nose. One or more relatively large flat disk-like plates of transparent plastic or the like were held in a sight opening in the face piece to serve as a window therein. By this means the eyes are allowed to focus under the water, which they could not do as easily were it not for the mask. Because water has a higher refractory index than air, however, a foreshortening effect occurs, making underwater objects appear closer and larger than they really are.
The problem of this foreshortening effect has been attacked in the past by making the lens system more complex, such as that shown in Simpson, U.S. Pat. No. 3,040,616. That patent shows a multiple lens system wherein water is permitted to enter behind a part of the system when the user is underwater. The purpose of this arrangement is to permit the user to see equally well when out of the water as when in. Since the diver usually takes his mask off when out of the water, however, such a structure is much more complex, and hence expensive, than necessary.
In using a mask described in another patent, Hagen, U.S. Pat. No. 3,672,750, a diver is required to look through several layers of material, necessarily having a refractive boundary between them. Further, the mask described in that patent provides convex lenses, which tend to invert the image being seen. And that mask does nothing to correct the color distortion inherent in underwater viewing. Correspondingly the Hagen patent also does not in any way mention the safety advantages of protecting workers from underwater ionizing and non-ionizing emissions.
This invention relates to improvements to the structure indicated above and to solutions to the problems raised or not solved thereby.